Gas separation is useful in many industries and can typically be accomplished by flowing a mixture of gases over an adsorbent material that preferentially adsorbs one or more gas components, while not adsorbing one or more other gas components. The non-adsorbed components are recovered as a separate product.
One particular type of gas separation technology is swing adsorption, such as temperature swing adsorption (TSA), pressure swing adsorption (PSA), partial pressure swing adsorption (PPSA), rapid cycle pressure swing adsorption (RCPSA), rapid cycle partial pressure swing adsorption (RCPPSA), and not limited to, but also combinations of the fore mentioned processes, such as pressure and temperature swing adsorption. As an example, PSA processes rely on the phenomenon of gases being more readily adsorbed within the pore structure or free volume of an adsorbent material when the gas is under pressure. That is, the higher the gas pressure, the greater the amount of readily-adsorbed gas adsorbed. When the pressure is reduced, the adsorbed component is released, or desorbed from the adsorbent material.
The swing adsorption processes (e.g., PSA and/or TSA) may be used to separate gases of a gas mixture because different gases tend to fill the micropore of the adsorbent material to different extents. For example, if a gas mixture, such as natural gas, is passed under pressure through a vessel containing an adsorbent material that is more selective towards carbon dioxide than it is for methane, at least a portion of the carbon dioxide is selectively adsorbed by the adsorbent material, and the gas exiting the vessel is enriched in methane. When the adsorbent material reaches the end of its capacity to adsorb carbon dioxide, it is regenerated by reducing the pressure, thereby releasing the adsorbed carbon dioxide. The adsorbent material is then typically purged and repressurized. Then, the adsorbent material is ready for another adsorption cycle.
The swing adsorption processes typically involve adsorbent bed units, which include adsorbent beds disposed within a housing configured with maintain fluids at various pressures for different steps in an adsorption cycle within the unit. These adsorbent bed units utilize different packing material in the bed structures. For example, the adsorbent bed units utilize checker brick, pebble beds or other available packing. As an enhancement, some adsorbent bed units may utilize engineered packing within the bed structure. The engineered packing may include a material provided in a specific configuration, such as a honeycomb, ceramic forms or the like.
Further, various adsorbent bed units may be coupled together with conduits and valves to manage the flow of fluids. Orchestrating these adsorbent bed units involves coordinating the cycles for each of the adsorbent bed units with other adsorbent bed units in the system. A complete cycle can vary from seconds to minutes as it transfers a plurality of gaseous streams through one or more of the adsorbent bed units.
Unfortunately, conventional processes for dehydration of natural gas streams are typically performed using large molecular sieve adsorbent beds, wherein the thermal swing cycle is hours long. This conventional process requires large and expensive high pressure adsorbent beds, a large inventory of adsorbent material, and involves large footprints and weights, capital investment and fuel usage for gas furnaces. Indeed, in these processes, the adsorption front progresses through the majority of the adsorbent bed's length, and desorption is accomplished using dry gas heated to over 500° F. (Fahrenheit) (260° C. (Celsius), which is heated with a fired furnace. The conventional TSA molecular sieve process uses high temperature purge gas (e.g., at or even above 500° F. (260° C.)) to completely dehydrate the adsorbent beds during each cycle. High temperature purge gas is used in conventional TSA molecular sieve process to minimize the volume of regeneration gas required. This process is driven by economic and expenditure considerations, because handling the regeneration gas volumes (e.g., via recycle compression or some other method) is more costly than simply heating the regeneration gas to a higher temperature. Thus, the regeneration gas temperature is limited to around 500° F. (260° C.) to avoid molecular sieve degradation. Yet, even limiting the regeneration gas to 500° F. (260° C.), the high temperature purge gas results in problems, such as hydrothermal degradation of the adsorbent particles and coke formation within the adsorbent bed leading to deactivation and associated downtime. Additionally, the use of a fired furnace in a natural gas plant is a safety concern that involves additional safety measures to manage.
In addition, for floating operations, the size and weight of conventional TSA molecular sieve process are problematic for stability and buoyance considerations. In particular, the excessive weight and footprint for conventional systems add to the complexity of the floating facility and increase the size of the facilities. Additionally, the floating facilities may be remotely located and may be difficult to access and resupply the equipment and fuel. Also, the additional size and complexity increase the capital investment costs along with the operating costs for the floating facilities. In addition, as noted above, the use of a fired furnace is further complicated by the limited space available.
Accordingly, there remains a need in the industry for apparatus, methods, and systems that provided an enhancements to the processing of streams to remove contaminants, such as processing the natural gas streams prior to liquefaction into an LNG feed stream. The present techniques provide a reduction in cost, size, and weight of facilities for natural gas dehydration prior to liquefaction. Further, a need remains for a dehydration process that does not use purge gases heated to over 500° F. (260° C.) and does not use fire heaters.